1. Field of the Invention
The present invention relates to an angular acceleration detection device that detects an angular acceleration acting about a detection axis.
2. Description of the Related Art
One type of angular acceleration detection device includes a rotating weight, a support beam, and a detection portion (see, e.g., Japanese Patent No. 2602300 and Japanese Unexamined Patent Application Publication No. 2010-139263). The support beam is disposed to extend in a direction orthogonal to a detection axis, and opposite end portions of the support beam are connected to the rotating weight and a fixed portion, respectively. When an angular acceleration acts about the detection axis in the angular acceleration detection device, the rotating weight is rotated (oscillated) with respect to the fixed portion by the action of a rotational inertial force generated upon application of the angular acceleration. The support beam is deformed with the rotation of the rotating weight, whereupon the detection portion detects stress generated in the support beam. Because the stress generated in the support beam changes depending on the angular acceleration acting on the rotating weight about the detection axis, the angular acceleration about the detection axis can be measured from a signal detected by the detection portion.
In the angular acceleration detection device described above, if the rotation of the rotating weight about the detection axis is out of balance, the rotating weight is caused to rotate by not only the rotational inertial force, but also a translational inertial force. In such a case, the translational inertial force becomes a factor of increasing noise of the detection signal, and detection accuracy of the angular acceleration about the detection axis degrades.
To ensure balance in the rotation of the rotating weight, the angular acceleration detection device is usually formed in a symmetrical shape with respect to the gravity center position of the rotating weight being a center. Japanese Patent No. 2602300 discloses a structure in which an annular rotating weight is supported from the inner side by a plurality of support beams, which are arranged symmetrically with respect to the gravity center position of the rotating weight being a center. Japanese Unexamined Patent Application Publication No. 2010-139263 discloses a structure in which a rotating weight is supported from the outer side by a plurality of support beams, which are arranged symmetrically with respect to the gravity center position of the rotating weight being a center.
In the related art described above, because the plural support beams bear, in a distributed manner, the inertial force exerted on the rotating weight, there has been a problem that, when the angular acceleration detection device is constituted to operate at a predetermined natural frequency, stress generated in each support beam per unit of angular acceleration decreases, and the detection accuracy of the angular acceleration degrades.
In consideration of the above-mentioned problems, it is conceivable to reduce the number of support beams for the purpose of obtaining higher detection accuracy with the angular acceleration detection device. However, there has been a limitation in reducing the number of support beams because of severe restrictions on the number and the arrangement of support beams from the viewpoint of ensuring the rotational balance of the rotating weight.